SASLAuthenticationStepResult.fail(response:error:)

Signal authentication failure. If data is provided, send it. A value of nil signifies sending no response at all, whereas a value of [] signifies sending an empty response, which may not be the same action depending on the underlying protocol. The provided error, if any, is surfaced. If none is provided, a generic failure is surfaced instead.

case fail(response: [UInt8]? = nil, error: (any Error)? = nil)